1. Technical Field
This invention relates to a power-supply device that supplies electrical power to a radar device adapted to detect an object on the basis of a Fourier transform of a beat signal, and relates to a radar system including the radar device and the power-supply device.
2. Related Art
A known vehicle-mounted radar system, as described in Japanese Patent Application Publication No. 2009-264952, includes a radar device that transmits and receives a continuous wave, generates a beat signal by mixing a received signal (reflected wave from an object) with its transmit signal, samples the beat signal, and then detects the object on the basis of a Fourier transform (FFT) of the beat signal. The radar system further includes a power-supply device that supplies electrical power to the radar device.
The power-supply device in the radar system disclosed in Japanese Patent Application Publication No. 2009-264952, which serves as a switching power-supply, converts electrical power from a vehicle battery into electrical power in a predefined voltage range by turning on and off a switcher in response to a switching clock, thereby supplying the power to the radar device.
The power-supply device disclosed in Japanese Patent Application Publication No. 2009-264952 further includes a signal selector that selects one of a plurality of switching clocks having mutually different frequencies and outputs the selected switching clock to the switcher.
More specifically, the signal selector disclosed in Japanese Patent Application Publication No. 2009-264952 receives a reference clock generated in a reference clock generation circuit provided external to the radar system, and a clock signal generated in a switching clock generator in the radar device, where a frequency of the clock signal is set to a Nyquist frequency (half a sampling frequency for sampling the beat signal). The signal selector outputs the reference clock as a switching clock for a prescribed period of time from the start of power supply to the whole radar system, and outputs the clock signal as another switching clock after the end of the prescribed period of time.
That is, in the radar system disclosed in Japanese Patent Application Publication No. 2009-264952, a frequency peak that corresponds to a switching frequency (i.e., the frequency of the clock signal) appears at ends of a frequency distribution given by the Fourier transform of the beat signal. This can prevent the frequency peak corresponding to the switching frequency from being erroneously detected as the object.
However, in practice, the frequency of the clock signal generated in the switching clock generator has a large error relative to the target frequency (for example, of the order of 100 kHz) because of low accuracy in the clock signal frequency.
In the radar system disclosed in Japanese Patent Application Publication No. 2009-264952, such a large error can increase a possibility that the frequency of the clock signal is included in a frequency band in which a frequency peak corresponding to the object can appear, and thus leads to erroneous detection of the frequency peak corresponding to the frequency of the clock signal as the frequency peak of an object.
In consideration of the foregoing, exemplary embodiments of the present invention are directed to providing a radar system capable of securely preventing erroneous detection of the frequency peak corresponding to the frequency of the clock signal as the frequency peak of an object.